In view of the purpose and functions of a circuit breaker, it is important that the contacts of a circuit breaker are separated quickly when circuit interruption is initiated. For multi-pole circuit breakers, a common trip bar or crossbar allows the poles of the circuit breaker to trip if not simultaneously, virtually simultaneously. The common trip bar or crossbar transfers the motion of one pole's trip lever to that of the other poles in the circuit breaker, causing them to trip as well. If the common trip bar or crossbar fits too loosely within one or more of the trip levers of a multi-pole circuit breaker, there may be insufficient motion of the poles' trip levers to trip the poles.
In a multi-pole circuit breaker with common trip bar or crossbar, an actuator in the first pole to trip drives the trip lever for that pole to a tripped position. That trip lever drives the common trip bar or crossbar which in turn drives the trip lever(s)for the remaining pole(s). If the remaining pole(s) contains a mechanism, that pole's trip lever typically engages a latch, releasing the mechanism(s) and causing that pole trip. Some trip lever/bar designs have trip bars which are not integral units such as when they are not molded together but the trip bar is separate from the levers. An advantage of multi-piece design is that it permits using electrically conducting materials, when required for strength or rigidity, to be used for the trip lever or bar, without risk of phase-to-phase shorting. Additionally, it allows breaker poles to be assembled individually then assembled together with the trip bar in place. One disadvantage of the multi-piece design is that because of the manufacturing tolerances of the parts, the trip bar can mate loosely with the levers. If the available driving motion is limited and the looseness of the fit between components of a multi-piece design is too great, the driven trip lever(s) may have insufficient motion to trip its pole(s).
For example, if a trip lever rotates about a pivot, it moves the bar and the driven trip lever through angular displacements. Looseness between the parts reduces the angular displacement at the driven trip lever. Prior art designs have attempted to compensate for the loss of motion using the following techniques.
One is to change the part that moves the driving trip lever to increase input motion to the assembly. This frequently requires expensive tooling changes and/or may change the part to such a degree that it won't work in other applications.
Another prior art design is to shorten the trip lever so the same input motion provides a greater angular rotation to the assembly, so the rotation lost due to looseness has less effect. However, the room required to accomplish this frequently does not exist, part interferences oftentimes result, or tooling changes are required.
Further, prior art attempts have been to specify lower tolerances for the mating parts but the part cost usually increases.